As is known, motor vehicles, and particularly trucks, are equipped with an air conditioning system, hereinafter referred to as the “main” air conditioning system, comprising a compressor, a condenser, an expansion valve, and an evaporator, which together define in known manner a main cooling circuit in which a cooling fluid flows. The compressor is driven by the vehicle engine, which must therefore be kept running for the compressor to operate when the vehicle is stationary. In addition to inefficient use of the engine, this obviously also results in increased fuel consumption and pollutant emissions.
By way of a solution to the problem, an auxiliary air conditioning system has been proposed comprising an auxiliary heat engine of lower power than the vehicle engine; and an auxiliary cooling circuit, in turn comprising an auxiliary compressor, condenser, expansion valve and evaporator. When the vehicle is stationary, the auxiliary engine need therefore simply be kept running. Besides consuming less fuel than the main vehicle engine, the auxiliary engine can also be run in maximum-efficiency conditions, thus minimizing consumption and pollutant emissions.
U.S. Pat. No. 5,528,901 describes an auxiliary air conditioning system of the type briefly described above, and which also comprises an auxiliary alternator driven by the auxiliary engine and connected to the vehicle battery to charge it while the auxiliary air conditioning system is running.
Though useful, the alternator battery charge function is only performed when the auxiliary air conditioning system is running, whereas modern trucks are equipped with high-consumption electric user devices which must be kept operative even when the vehicle is stationary and regardless of whether or not the air conditioning system is running. Typical examples of such devices are satellite security devices, which draw current when the vehicle is parked and the air conditioning system may be turned off.